Review: changing (shared) heritability of ASD and ADHD across the lifespan

European Child & Adolescent Psychiatry, Feb 2016

Nanda N. J. Rommelse, Catharina A. Hartman

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Review: changing (shared) heritability of ASD and ADHD across the lifespan

Eur Child Adolesc Psychiatry Review: changing (shared) heritability of ASD and ADHD across the lifespan Nanda N. J. Rommelse 0 1 2 Catharina A. Hartman 0 1 2 0 Department of Psychiatry, Interdisciplinary Center of Psychopathology and Emotion Regulation (ICPE) and Research School of Behavioral and Cognitive Neuroscience, University of Groningen, University Medical Center Groningen , Groningen , The Netherlands 1 Karakter, Child and Adolescent Psychiatry University Center , Nijmegen , The Netherlands 2 Department of Psychiatry, Donders Institute for Brain, Cognition and Behavior, Radboud University Medical Center , Nijmegen , The Netherlands 3 Nanda N. J. Rommelse been strongly focused on childhood. The age of onset for ASD and ADHD is nearly always in childhood ([18]; but see [17]), which is the likely reason for this bias. However, given that it is already well known that developmental changes take place in both ADHD and ASD symptom domains separately, a focus beyond childhood is needed to further understand the potentially changing etiology of ADHD-ASD co-occurrence. Introduction Autism spectrum disorder (ASD) and attention-deficit/ hyperactivity disorder (ADHD) frequently co-occur. In clinical practice, we daily struggle deciding if one, or the other, or both disorders, best describe the child’s problems. A strong body of literature has convincingly shown that large overlap exists regarding genetic factors [ 6, 11, 26, 29 ]. However, this genetic overlap may significantly depend on age. It is well known that genetic influences on behavior are not at all constant during development and continuously co-act and interact with environmental factors influencing behavioral functioning [ 1, 30 ]. For example, increasing heritability can result from amplification, whereby early genetic influences become stronger across time. As a second example, genetic influences may be stable; yet novel genetic influences may emerge with time while early genetic influences may decrease [ 2 ]. Despite everyone’s awareness of change in the (genetic) mechanisms underlying the development of an individual until elderly age in typical development, studies on neurodevelopmental disorders like ADHD and ASD have Several longitudinal twin studies on ADHD symptoms report that new, age-specific genetic effects influence ADHD symptoms in adolescence and adulthood, suggesting that ADHD symptoms are a developmentally complex phenotype characterized by both continuity and change across the life span [ 3, 9, 12, 13, 19 ]. In addition, only a modest overlap between longitudinal genetic effects underlying both symptom domains (inattention versus hyperactivity/impulsivity) appears present, suggesting it is necessary to study both separately. Moreover, several longitudinal studies report that subgroups may be formed based on various combinations of symptoms in both domains across the longitudinal course that likely has partly distinct genetic underpinnings ([ 7, 14, 25 ]). These findings strongly suggest that genetic effects implicated in childhood ADHD may not at all be directly comparable to those that influence ADHD in adulthood. This concurs with a review on molecular genetics in adult ADHD, where it was concluded that only some genes potentially related to childhood ADHD have been replicated in adults with the disorder [ 8 ]. In addition, in some cases the same genes were implicated, but different alleles increased the risk for ADHD in children versus adults (for instance, the 10-repeat in the dopamine transporter gene [DAT1] increased the risk for ADHD in children, but decreased the risk in adults) [ 8 ]. Note though that currently there are no unequivocal molecular genetic findings for ADHD in either childhood or adulthood, possibly contributing to these results. Moffitt et al. [ 17 ] reported about adults aged 38 years presenting with an ADHD symptom picture, who did not have childhood ADHD as assessed in early adolescence. They did not share the genetic and neuropsychological alterations of those who did have the childhood diagnosis. Even during adolescence, environmental effects (like smoking) controlled for genetic confounders may have a significant impact on future development of ADHD symptoms [ 33 ], illustrating the developmentally sensitive nature and non-static genetic influence of the ADHD phenotype beyond childhood. Heritability of ASD across the life span In comparison to ADHD, fewer longitudinal, genetically informative studies have examined the developmental nature of ASD symptoms into adolescence or even adulthood. Specifically, studies on the presence of new genetic effects occurring in late adolescence or adulthood compared to childhood—as reported for ADHD—have not yet been conducted. In addition, to what extent the different symptom domains of ASD are influenced by distinct genetic effects over time is unknown. A study reporting on the stability of genetic effects from childhood into early adolesce (...truncated)


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Nanda N. J. Rommelse, Catharina A. Hartman. Review: changing (shared) heritability of ASD and ADHD across the lifespan, European Child & Adolescent Psychiatry, 2016, pp. 213-215, Volume 25, Issue 3, DOI: 10.1007/s00787-016-0830-9